I did get a Twiskee lock apart. It was a basket case from the start because the shackle had been broken off right at the heel and the key would not do much of anything. I started by milling the toe side clean, and discovered the faint outline of a plug. This was drilled and tapped then a screw was used to pull out the plug and a spring:

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I couldn't get anything else out due to corrosion so I decided to attack the top next, but filed down the bottom so it would be fairly flat and rest nicely on the milling vise. But that made me notice an annular plug:

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So this ring was drilled and tapped (but I guessed wrong, trying 4-40 which was too big, and tried again with 2-56) and pulled out. The locking parts were removed, the shackle remnant was released, and the locking bar pushed out. Here's everything arranged more or less in order:

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On the right, 4th from the end, the tall item I'll call the "warding plug". It's what contains the the twisted slot for the key, and in this model some protrusions that match grooves on the key. On the left end of that string of parts is an actuator cup which has a pin that cooperates with a groove in the locking bar (top item in the vertical string of parts). Cleverly, the locking bar has a spring-loaded pin that needs to be depressed before it can moved by the actuator. That's why the key has the small tip which extends through a hole in the actuator, to move the pin out of the way.

Most parts are non-magnetic and thus brass or other alloy, including the springs and warding plug. But the shackle and locking bar are steel (also the key) and that's what apparently caused the lock to sieze up followed by destructive removal.

I have another example that is siezed up and missing the key, and another that is complete and works well but the key looks like a cheap "recent" one compared to the one shown above.

A problem of sorts with the one that works is that it unlocks by twisting the key counter-clockwise. I always forget that and most padlocks unlock the other direction. I wonder if that's one reason these were not more popular.

I also would like to know how the warding plug was manufactured.